1. Field of the Invention
This invention relates generally to methods and apparatus for earth excavation with drills and augers, and more particularly to a method and apparatus for rapid earth excavation utilizing drills and augers having soft cutting edges and/or control of the torque and weight of the boring apparatus to prevent damage to buried pipe, cable, and other underground objects.
2. Brief Description of the Prior Art
A considerable portion of the operating budget of gas, electric, and telecommunications industries is spent to maintain and repair the efficiency and safety of the buried distribution system connecting supplies to the end user. It is estimated that the U.S. gas distribution industry alone must maintain an estimated 866,000 miles of distribution mains and 563,000 miles of services with the network expanding at a rate of 9,000 miles a year. The installation, repair, and maintenance of these mains and services is costly, requiring a significant amount of manpower and equipment. It is estimated that the gas industry alone will dedicate over 450 million dollars in 1988 to repair leaks, replace aging lines, and to install corrosion protection.
Several methods are presently used to expose buried pipe, cables, and other utilities for repair and maintenance. Most common among these methods are backhoes and hand digging Backhoes offer the advantage of high speed and minimal setup time but can cause serious damage to utilities contacted by the bucket while it is digging. The size of the excavation produced by the backhoe is often substantially larger than necessary, which increases the cost of restoration. Records filed with the Department of Transportation show that 60% of gas pipe incidents which occurred between 1974 and 1984 were caused by large excavation equipment.
Conversely, hand digging is effective in minimizing damage to buried utility lines, but is slow and highly labor intensive. Vacuum and soft excavators employing vacuum for spoil removal are limited in the range of soils in which they are effective and the speed at which the lines are uncovered.
There are several patents which disclose various methods and apparatus for controlling the torque of the drilling or boring apparatus.
Bricken, U.S. Pat. No. 1,776,779 discloses a well drilling and pumping apparatus with torque control.
Hawk, U.S. Pat. No. 1,904,765 discloses a method of torque control and automatic drill control.
Vanderzee, U.S. Pat. No. 2,594,098 discloses a portable, truck-mounted drilling rig with torque control.
Pokorny, U.S. Pat. No. 2,734,722 discloses a post hole driller with hydraulic controls but no flexible cutting surface or auger.
Goodrich, U.S. Pat. No. 2,981,403 discloses an auger with flexible flights but does not teach using soft flexible materials in the cutting surface.
Rumpp, U.S. Pat. No. 4,458,769 discloses a rock drill having a helical surface for removing cuttings but does not teach using soft flexible materials in the cutting surface or on the flights of an auger.
Warren et al, U.S. Pat. No. 4,660,656 discloses a method and apparatus for controlling torque and a rotary earth drilling bit but does not teach using soft flexible materials in the cutting surface.
Muller, U.S. Pat. No. 4,699,226 discloses an interchangeable conveying spiral which can be removable mounted on a drill shaft for removing rock cuttings out does not teach using soft flexible materials in the cutting surface or on the flights of an auger.
Snyder, U.S. Pat. No. 2,714,500 discloses an impact drill with flexible blades which are used only for a wiping action on the side wall of the hole being drilled. There is no suggestion of using soft flexible materials in the cutting surfaces.
The present invention is distinguished over the prior art in general, and these patents in particular by a rapid earth excavation method and apparatus utilizing drills and augers having soft polymeric material on the cutting edges, control of the torque and weight of the boring apparatus, or an indicator mounted forward of and below the leading cutting surface of the auger to prevent damage to buried pipe, cable, and other underground objects.